PERSPECTIVES ON FAILED RIFTING AND FAST DRIFTING USING NEW AND OLD PALEOMAGNETIC DATA FROM THE MIDCONTINENT RIFT

There is a storied and fruitful history of paleomagnetic study in the 1.1 Ga Midcontinent Rift. This work has provided much of the foundation for lithostratigraphic correlation of units across the rift and for reconstructing important aspects of late Mesoproterozoic paleogeography, such as the assembly of supercontinent Rodinia. Leveraging stratigraphic context to improve paleomagnetic interpretation from the succession at Mamainse Point has provided strong support for the hypothesis that shallower paleomagnetic inclinations in younger rift rocks relative to older ones is the result of the equatorward motion of Laurentia, rather than an artifact of large non-axial dipole contributions to the geomagnetic field. This interpretation has been supported with a data set that now encompasses more than 100 flows across 4 polarity zones at Mamainse Point and is being further addressed by the development of data from 45 flows of the Osler Volcanic Group. As a result, the progressive decrease in paleolatitude through time provides a powerful chronological constraint (in addition to geomagnetic polarity) on the history of rift volcanics, intrusives, and sediments. Furthermore, we can more confidently use the rich repository of information in rift volcanics and intrusives to address outstanding questions concerning paleogeography and the ancient strength and geometry of the geomagnetic field. Efforts to further refine the “Logan Loop” and “Keweenawan Track” apparent polar wander paths can proceed with a nuanced approach to the pairing of paleomagnetic data with high precision U/Pb ages in order to further constrain rapid plate motion, and provide a calibrated record to advance quantitative reconstructions of late Mesoproterozoic paleogeography.